The present disclosure relates to circuit arrangements for a multimode mobile telephone for transmitting/receiving signals to/from various mobile radio networks.
In many fields, such as with multimode mobile telephones, a linear signal amplification with a high output efficiency is required. One way of achieving a linear signal amplification is to combine a non-linear power amplifier (PA) that has a non-linear curve, with a predistorter. The predistorter distorts the input signals so that the complete system consisting of a predistorter and nonlinear power amplifier again has a substantially more linear behavior than just a power amplifier. This method of application is known as predistortion. The combination of the predistorter curve of the input signal and the non-linear amplification curve results overall in a linear curve of the transmitting system and thus a linear signal amplification. One problem with this method of application occurs due to the ageing of components or the temperature-dependence of components. The effects of such phenomena change the linearity of the transmission system.
To correct these undesirable effects using digital adaptive predistortion, the envelope of the amplified signal is regained with the aid of a measuring branch, or feedback branch. The curve of the predistorter is accordingly adapted. The feedback branch consists mainly of a coupler, a demodulator and an analog-digital converter (ADC).
A disadvantage of this method of digital adaptive predistortion is that the feedback branch involves additional cost, installation space and power consumption. For this reason, no linearization methods for power amplifiers requiring a complex feedback branch have so far been realized in commercial systems.